Once you find a company online who supplies the chemical you want, you contact them by phone, e-mail or fax and ask them for quotes for the quantities you require. For industrial quotes - it depends on how much you want to buy before they will give you a quote or pass you on to a smaller distributor. i.e. if you want 2000kg of solvent, then the manufacturers may give you a quote direct or pass you onto a main disty.. if you want a 200 kg barrel, then they will send you to a disty or one of their smaller dealers.
In short - ring them up and ask them.